Soil organic carbon (SOC) dynamics in croplands is a crucial component of global carbon (C) cycle. Depending on local environmental conditions and management practices, typical C input is generally required to reduce or reverse C loss in agricultural soils. Changes in the soil organic carbon (SOC) stock are determined by the balance between the carbon input from organic materials and the output from the decomposition of soil C. The fate of SOC in cropland soils plays a significant role in both sustainable agricultural production and climate change mitigation. Tillage systems can influence C sequestration by changing aggregate formation and C distribution within the aggregate. Results showed that the soil organic carbon (SOC) stock in bulk soil was 40.2-51.1% higher in the 0.00-0.05 m layer and 11.3-17.0% lower in the 0.05-0.20 m layer in NT system no-tillage without straw (NT-S) and with straw (NT+S), compared to the MP system moldboard plow without straw (MP-S) and with straw (MP+S), respectively. Residue incorporation caused a significant increment of 15.65% in total water stable aggregates in surface soil (0– 15 cm) and 7.53% in sub-surface soil (15–30 cm).
Trang 1Review Article https://doi.org/10.20546/ijcmas.2019.804.259
Conservation Tillage and Residue Management towards Low Greenhouse Gas Emission; Storage and Turnover of Natural Organic Matter in Soil
under Sub-tropical Ecosystems: A Review
S.K Tomar 1* , N.C Mahajan 2 , S.N Singh 3 , Vinay Kumar 4 and R.K Naresh 5
1
KVK Belipar, Gorakhpur, 3 KVK Basti, 4 KVK Akbarpur, Narendra Dev University of
Agriculture & Technology, Kumarganj, Ayodhya, U.P., India 2
Institute of Agricultural Sciences; Department of Agronomy, Banaras Hindu University,
Varanasi-(U.P), India 5
Department of Agronomy, Sardar Vallabhbhai Patel University of Agriculture & Technology,
Meerut, (UP), India
*Corresponding author
A B S T R A C T
International Journal of Current Microbiology and Applied Sciences
ISSN: 2319-7706 Volume 8 Number 04 (2019)
Journal homepage: http://www.ijcmas.com
Soil organic carbon (SOC) dynamics in croplands is a crucial component of global carbon (C) cycle Depending on local environmental conditions and management practices, typical C input is generally required to reduce or reverse C loss in agricultural soils Changes in the soil organic carbon (SOC) stock are determined by the balance between the carbon input from organic materials and the output from the decomposition of soil C The fate of SOC in cropland soils plays a significant role in both sustainable agricultural production and climate change mitigation Tillage systems can influence C sequestration by changing aggregate formation and C distribution within the aggregate Results showed that the soil organic carbon (SOC) stock in bulk soil was 40.2-51.1% higher in the 0.00-0.05 m layer and 11.3-17.0% lower in the 0.05-0.20 m layer in NT system no-tillage without straw (NT-S) and with straw (NT+S), compared to the MP system moldboard plow without straw (MP-S) and with straw (MP+S), respectively Residue incorporation caused a significant increment of 15.65% in total water stable aggregates in surface soil (0–
15 cm) and 7.53% in sub-surface soil (15–30 cm) In surface soil, the maximum (19.2%) and minimum (8.9%) proportion of total aggregated carbon was retained with >2 mm and 0.1–0.05 mm size fractions, respectively DSR combined with zero tillage in wheat along with residue retention (T 6 ) had the highest capability to hold the organic carbon in surface (11.57 g kg -1
soil with the highest stratification ratio of SOC (1.5) A considerable proportion of the total SOC was found to be captured by the macro-aggregates (>2–0.25 mm) under both surface (67.1%) and sub-surface layers (66.7%) leaving rest amount in micro- aggregates and ‗silt + clay‘ sized particles Soil tillage practices have a profound influence on the greenhouse gas (GHG) balance However there have been very few integrated studies on the emission of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) and soil biophysical and chemical characteristics under different soil management systems Tillage played a significant role in the flux of
CO 2 and CH 4 In contrast, N 2 O flux was determined mainly by microbial biomass carbon and soil moisture content Compared with other treatments, NT significantly reduced CH 4 emission among the rice growing seasons However, much higher variations in N 2 O emission were observed across the rice growing seasons due to the vulnerability of N 2 O to external influences The amount of CH 4 emission in paddy fields was much higher relative to N 2 O emission Conversion of CT to NT significantly reduced the cumulative
CH 4 emission for both rice seasons compared with other treatments The mixing of residues/surface retention into the soil increases SOM mineralisation due to greater exposure to microbial decomposers and optimal moisture and temperature regimes Soil disturbance by tillage leads to destruction of the protective soil aggregate This in turn exposes the labile C occluded in these aggregates to microbial breakdown The present study found that SOC change was significantly influenced by the crop residue retention rate and the edaphic variable of initial SOC content
Trang 2Introduction
Agriculture accounts for approximately 40-50
% of the earth‘s surface is managed for
agricultural purposes and contributes 10-12 %
of global greenhouse gas (GHG) emissions,
around 5.1-6.1 Pg CO2 -eq yr-1 in 2005 (Smith
et al., 2007a) This is made up of 3.3 Pg CO2
-eq yr-1 from methane (CH4) and 2.8Pg CO2
-eq yr-1 from nitrous oxide (N2O) emissions
Although there are large exchanges of carbon
dioxide (CO2) between the atmosphere and
agricultural ecosystems, emissions are
thought to be roughly balanced by uptake,
giving a net flux of only around 0.04 Pg CO2
yr-1, less than 1 % of global anthropogenic
CO2 emissions (Smith et al., 2007a) Land use
change is accounted for separately, but
change to cultivated land is thought to
contribute a further 5.9 ± 2.9PgCO2-eq yr-1,
6-17 % of total global GHG emissions (Bellarby
et al., 2008) If indirect emissions from
agrochemical production and distribution and
on-farm operations, including irrigation, are
also included, an extra 0.4-1.6 Pg CO2-eq yr-1
(0.8-3.2 %) can be attributed to agriculture,
meaning that, in total, direct and indirect
emissions from agricultural activity and land
use change to agricultural use could
contribute as much as 32.2 % of all GHG
emissions (Bellarby et al., 2008) Agriculture
is the main source of global non CO2 GHG
emissions, contributing around 47 % of
anthropogenic CH4 emissions and 58 % of
N2O, although there is a large degree of
uncertainty around estimates for both
agricultural contribution and total
anthropogenic emissions The main sources,
N2O from soils and CH4 from enteric
fermentation, make up around 70 % of
non-CO2 emissions from the sector, with biomass
burning, rice cultivation, and manure
management, accounting for the remainder
(Smith et al., 2007a) Conservation tillage is
one among many different mitigation options
suggested to reduce GHG emissions from
agriculture Conservation tillage practices such as reduced/minimum/zero tillage, direct drilling and strip cropping are also widely recommended to protect soil against erosion
and degradation of structure (Petersen et al.,
2011), create greater aggregate stability
(Fernandez et al., 2010; Zotarelli et al., 2007)
increase soil organic matter content, enhance
sequestration of carbon (Six et al., 2000) mitigate GHG emissions (Kong et al., 2009) and improve biological activity (Helgason et
al., 2010)
Minimum tillage practices have been reported
to reduce GHG emissions through decreased use of fossil fuels in field preparation and by increasing carbon sequestration in soil
(Petersen et al., 2008) The crop residues
accumulated on the soil surface under reduced tilled conditions may result in carbon being lost to the atmosphere upon decomposition
(Petersen et al., 2008) Furthermore, climate
change mitigation benefits such as reduced
CO2 emissions, by virtue of increased sequestration of carbon and increased CH4
uptake under reduced tillage, could be offset
by increased emissions of N2O, a greenhouse gas with higher warming potential than both
CO2 and CH4 (Hermle et al., 2008; Chatskikh
and Olesen, 2007) Increased N2O emissions have been linked to increased denitrification under reduced tillage due to the formation of micro-aggregates within macro-aggregates
that create anaerobic micro sites (Hermle et
al., 2008) with increased microbial activity
leading to greater competition for oxygen (West and Marland, 2002)
Reduction of tillage can also create increased soil densification and a subsequent decrease
in the volume of macro-pores (Schjønning and Rasmussen, 2000) leading to reduction in gaseous exchange Soil aggregation and the resultant geometry of the pore structure are vitally important characteristics affected by tillage practices which impact on the physico-
Trang 3chemical and hydro-thermal regime in soil,
and ultimately crop yield Additionally, the
effect of tillage on the environment varies
across farms geographically since the impacts
of cultivation on soil organic matter and net
greenhouse balance depends on soil type,
climatic variables and management
(Chatskikh and Olesen, 2007)
Natural organic matter in soils is the largest
carbon reservoir in rapid exchange with
atmospheric CO2, and is thus important as a
potential source and sink of greenhouse gases
over time scales of human concern (Fischlin
and Gyalistras, 1997) SOM is also an
important human resource under active
management in agricultural and range lands
worldwide Questions driving present
research on the soil C cycle include: Are soils
now acting as a net source or sink of carbon
to the atmosphere? What role will soils play
as a natural modulator or amplifier of climatic
warming? How is C stabilized and
sequestered, and what are effective
management techniques to foster these
processes? Answering these questions will
require a mechanistic understanding of how
and where C is stored in soils SOM quantity
and composition reflect the long-term balance
between plant carbon inputs and microbial
decomposition The processes underlying soil
carbon storage and turnover are complex and
dynamic, involving influences from global to
molecular scales At the broadest level, SOM
cycling is influenced by factors such as
climate and parent material, which affect
plant productivity and soil development At a
more proximate level, factors such as plant
species and soil mineralogy affect
decomposition pathways and stabilization
processes The molecular characteristics of
SOM play a fundamental role in all processes
of its storage and stability
Historical global estimates for the top meter
of soil vary from 800 Pg C to 2,400 Pg C,
converging on the range of 1,300–1,600 Pg C
to 1 m Batjes (1996) estimated that an additional 900 Pg C is stored between 1 and 2
m depth, and Jobbágy and Jackson (2000) revised that estimate to 500 Pg between 1 and
2 m and another 350 Pg between 2 and 3 m depth Global organic carbon stocks to 3 m are currently estimated at 2,300 Pg, with an additional 1,000 Pg contained in permafrost and peat lands (Jobbagy and Jackson, 2000;
Zimov et al., 2006) In this review paper we
sought to evaluate the impact of conservation tillage on storage and turnover of natural organic matter in soil and GHG emissions
We hypothesized that conservation tillage improves storage and turnover of natural organic matter in soil and reduces GHG emissions compared with conventional tillage through the enhanced development of the soil carbon associated with less anthropogenic disturbance
Reicosky and Archer (2007) reported that the
CO2 released immediately following tillage increased with ploughing depth and in every case was substantially greater than that from the no-tillage treatment Intensive soil cultivation breaks down soil organic matter (SOM), producing CO2, and consequently reduces the total C content There are many reports suggesting that soil tillage accelerates organic C oxidation, releasing large amounts
of CO2 to the atmosphere over a few weeks
(La Scala et al., 2008) Conservation tillage
has been shown to result in a greater percentage of soil present in macro-aggregates and a larger proportion of carbon associated with micro-aggregates compared to
that in conventional ploughing (He et al.,
2011) Under conventional ploughing, aggregates are readily broken down prior to micro-aggregate formation This leads to a reduction in the proportion of C that is more protected in micro-aggregates and thus to the
macro-loss of recalcitrant SOC (Chivenge et al., 2007) Li et al., (2011) investigated methane
Trang 4emission patterns in a double-rice cropping
system under conventional tillage and
no-tillage in south-east China, where no-no-tillage
reduced seasonal methane fluxes by 29% and
68% for the early and late rice, respectively
Ahmad et al., (2009) also found that
no-tillage significantly reduced methane
emissions from paddy fields compared to
conventional tillage (Fig 1, 2 and 3)
Sarkhot et al., (2012) reported that the
prepared nutrient enriched bio-char by
shaking the bio-char with dairy manure
effluent for 24 h, which increased the C and N
content of the bio-char by 9.3% and 8.3,
respectively When the untreated bio-cha and
N enriched bio-char were added to a soil in
eight week incubation, the reduction in
availableNH4+-N and NO3 —
N content was observed, suggesting the possibility of N
immobilization Still, N enriched bio-char
could be used as a slow release N fertilizer
The net N nitrification rates in the CK, 1%
BC and 3% BC treatments also peaked at day
25, then dramatically decreased and stayed at
a very low level (0.35–0.42mg/(kg d)) at the
end of incubation
Sander et al., (2014) reported that
incorporation of rice residues immediately
after harvest and subsequent aerobic
decomposition of the residues before soil
flooding for the next crop reduced CH4
emissions by 2.5–5 times and also improved
nutrient cycling in paddy field It was also
reported that residue incorporation
accelerated CH4 and N2O emissions from
irrigated rice field compared to residues left
on the soil surface The open burning of crop
residues emits CO2, CH4, and N2O
Mangalassery et al., (2014) also found that
neither ammonium (NH4-N) nor nitrate (NO3
-N) content in soil was affected by tillage Soil
from the upper 10 cm contained significantly
higher NH4-N than the 10–20 cm layer
Nitrate (NO3-N) followed a similar trend to
NH4-N Tillage type and duration did not influence the NO3-N content Soil depth significantly influenced NO3-N content with highest amount in the surface layer (0–10 cm) under both zero tillage and conventional tillage Considering the GHGs together, tilled soil produced 20% greater net global warming than zero tilled soil indicating a potential for zero tillage system to mitigate climate change after only 5 to 10 years since conversion Del
Grosso et al., (2005) also reported a 33%
reduction in global warming potential under zero tillage (0.29 MgCha-1yr-1) compared with tilled soil (0.43 Mg C ha-1 yr-1) for major non-rice cropping systems Also in sub-tropical conditions, zero tillage has been found to
reduce GWP by c 20% (Pivea et al., 2012)
Residues management and crop rotations can affect N2O emissions by altering the availability of NO3 −
in the soil, the decomposability of C substrates (Firestone and Davidson, 1989) The reduction of N2O to
N2 is inhibited when NO3 −
and labile C
concentrations are high (Senbayram et al.,
2012) The retention of crop residues and higher soil C in surface soils with CA play major roles in these processes Under anaerobic conditions associated with soil water saturation, high contents of soluble carbon or readily decomposable organic matter can significantly boost de-nitrification
(Dalal et al., 2003) with the production of
N2O favoured with high quality C inputs (Bremner, 1997) The quantity and quality of residues or cover crops of CA systems can also affect N2O emissions Legume residues can result in higher N2O–N losses (Millar et
al., 2004) than those from non-legume, low N
residues (Aulakh et al., 2001) Crop residues
may affect CH4 oxidation in upland soils and emission patterns in flooded soils differently depending on their C/N ratio; residues with a high C/N ratio have little effect on oxidation while residues with a narrow C/N ratio seem
to inhibit oxidation (Hiitsch, 2011) Grace et
Trang 5al., (2012) estimated an average of 29.3 Mg
ha−1 of GHGs emitted over 20 years in
conventional rice-wheat systems across the
IGP; this decreased by only 3% with the
widespread implementation of CA
Agricultural practices such as tillage and
fertilization have to be considered Food
systems alone – everything from growing
plants to the disposal of biomass – contribute
to 19–29% of global anthropogenic GHG
emissions Of this, 80–86% relate to
agricultural production (including indirect
emissions associated with land-cover change),
albeit with significant regional variation
(Vermeulen et al., 2012) On agricultural
sites, N2O emissions from legume-N were
significantly lower than fertilizer-N derived
N2O emissions (Schwenke et al., 2015)
Gupta et al., (2016) revealed that the GWP
(CH4 + N2O) of wheat–rice systems varied
from 944 to 1891 kg CO2 eq ha-1 and 1167–
2233 kg CO2 eq ha-1 in the first and second
years of wheat–rice cropping respectively
The combination of ZTW followed by DSR
showed significantly low GWP than other
combination of wheat and rice treatments
These combinations led to about 44–47%
reductions in GWP over the conventional
CTW-TPR system in both the years The
order of GWP among the different
combination of treatments was as follows:
(ZTW + RR) - DSR < DSR <
ZTW-IWD < ZTW + NOCUTPR + NOCU <
CTWTPR < ZTW-TPR in both the years The
share of rice in total GWP was 72–81% in
those combinations in which TPR was a
treatment while it varied from 56 to 65%
where DSR was a treatment These results
indicate that adoption of ZTW followed by
DSR in the IGP in place of conventional
CTW-TPR can be an efficient low carbon
emitting option With the development of new
drills, which are able to cut through crop
residue, for zero-tillage crop planting, burning
of straw can be avoided, which amounts to as
much as 10 tons per hectare, potentially reducing release of some 13–14 tons of
carbon dioxide (Gupta et al., 2004)
Elimination of burning on just 5 million hectares would reduce the huge flux of yearly
CO2 emissions by 43.3 million tons (including 0.8 million ton CO2 produced upon burning of fossil fuel in tillage) Zero-tillage on an average saves about 60 l of fuel per hectare thus reducing emission of CO2 by 156 kg per
hectare per year (Grace et al., 2003; Gupta et
al., 2004) Sah et al., (2014) revealed that the
CO2 emissions conventionally tilled (CT) wheat emitted the highest amount of CO2 (224
kg ha-1) followed by PRB (146 kg ha-1) and the lowest from ZT (126 kg ha-1) The highest
CO2 emission through CT attributed to higher tractor usage on land preparation and more pumping time on irrigation However, ZT and PBP wheat emitted lower CO2 to the atmosphere by 43.7 % and 34.9 %, respectively, as compared to CT
Conservation tillage practices decreased the exposure of un-mineralized organic substances to the microbial processes, thus reducing SOM decomposition and
CO2 emission Apart from C, other greenhouse gases (GHGs) notably, nitrous oxide (N2O) and methane (NH4), have been reported to be influenced by tillage regimes (Steinbach and Alvarez, 2006) About 38% of the emissions to the atmosphere can be ascribed to nitrous oxide from soils (Bellarby
et al., 2008) while methane is considered as
the most potential greenhouse gas after carbon dioxide (IPCC, 2001) Significantly higher N2O emissions from ploughed than no-
tilled sites has been reported by Kessavalou et
al., (1998) The higher aeration in tilled soil
increases oxygen availability, possibly resulting in increased aerobic turnover in the soil and thus an increased potential for
gaseous emissions (Skiba et al., 2002) Seidel
et al., (2015) compared the ratio between
greenhouse gas emissions from inputs and
Trang 6crop output across organic and conventional
cropping systems and suggests that a legume
tilled management exhibited the best ratio
(59%) followed by manure tilled (63%),
manure no till (65%), legume no till (84%)
and conventional till (90%) as a per-cent of
the GHG emissions from conventional no till
management
Several of the agricultural and forestry GHG
mitigation options provide ancillary
co-benefits to the agricultural sector and to
society, making them somewhat unique in
their ability to address climate change
simultaneously with other pressing social and
environmental issues This has earned these
reductions the title of ―charismatic carbon
credits.‖ Increasing soil C also increases
available plant nutrients; considering the
nutrient supplying capacity of just N, P, S,
a1% increase in soil organic matter content
(equivalent to 21 Tons of CO2) would
translate to 75 lb N, 8 lb P and 8 lb of S per
acre (Rice et al., 2007)
CO2 in the atmosphere is in a constant state of flux among its repositories, or ―sinks‖; this is called the Carbon Cycle The movement, or
―flux,‖ of carbon between the atmosphere and the land and oceans sinks is dominated by natural processes, such as plant photosynthesis While these natural processes can absorb some of the net 6.3 billion metric tons of human-produced CO2 emissions emitted each year (about 2 billion metric tons are absorbed by the ocean and 1 billion by terrestrial systems, including soils), that leaves an estimated 3.2 billion metric tons that are added to the atmosphere annually The Earth‘s positive imbalance between emissions and absorption of GHG has resulted in the increased concentration of greenhouse gases in the atmosphere This causes global climate change
Turnover time and dynamics of soil organic matter
Cambardella and Elliott, (1994) reported that the turnover time of POC ranged from 5 to 20 years in cultivated grassland soils The reason might be that after cultivation of virgin black soils, soybean (C3 crop) residues provided an extra source of organic matter input in addition to corn-derived C (C4 crop) It might also be due to a certain amount of black C in
POC (Knicker et al., 2005) The mean
turnover time indicated faster turnover of SOC in coarse fraction than that in fine fraction We suggested that short-term NT did not significantly affect the turnover time of SOC The turnover time of SOC was even longer in MP plots because of the incorporation of returned crop residues into soils Thus, the short-term impact of no tillage was firstly shown in the coarse-size fractions (POC) The distribution of C3–C mainly in fine particles (silt plus clay) indicated that the turnover of SOC in coarse-size fraction was faster under tillage practices Regardless of residue type, mineralization of SOM
Trang 7increased up to from 50 to 90% due to
addition of low and high levels, respectively,
whereas residue addition was increased 3.6
times Therefore, the amount of primed CO2
decreased per unit of applied residue This
was also reported by Guenet et al., (2010) and
Xiao et al., (2015)
Zhu et al., (2015) revealed that the soil total
organic C (TOC) and labile organic C fraction
contents were higher under the straw return
treatments compared to the no straw return
treatment (0% S) at a 0–21 soil depth The
50% annual straw return rate (50% S) had
significantly higher soil TOC, dissolved
organic C(DOC), easily oxidizable C (EOC),
and microbial biomass C (MBC) contents
than the 0% S treatment at a 0–21 cm depth
All of the straw return treatments had a
significantly higher DOC content than the
0%S treatment at a 0–21 cm depth, except for
the 100% only rice straw return treatment
(100% RS) Wang et al., (2015) also found
that in the early paddy field, the average
values of the total SOC, LFOC, DOC and
MBC concentration in the top 40cm soil were
significantly higher in the straw application
plots than in the controls, by 7.2% 8.8%,
15.6%, and 128.6%, respectively Wright et
al., (2007) reported that in the 0-5 cm soil
depth, no-tillage increased
macro-aggregate-associated OC as compared to conventional
tillage Macro-aggregates accounted for
38-64, 48-66, and 54-71% of the total soil mass
in the 0-5, 5-10, and 10-20 cm soil depths,
respectively The corresponding proportions
of the silt+clay fraction were 3-7, 2-6, and
1-5%, respectively Proportions of
macro-aggregates were increased with reduction of
soil tillage frequency For the 0-5 cm soil
depth, treatments NT and 4T had significantly
higher mass proportions of macro-aggregates
(36 and 23%, respectively) than that of
treatment With additions of crop residues, the
amount of macro-aggregates increased in all
tillage treatments Conservation tillage
significantly increased SOC concentration of bulk soil in the 0−5 cm soil layer This increase in SOC concentration can be attributed to a combination of less soil disturbance and more residues returned to the
soil surface under conservation tillage (Du et
al., 2010; Dikgwatlhe et al., 2014) Alvarez et al., (2009) also found that NT increases SOC
and total N concentrations in the first centimetres of the soil profile because NT
maintains surface residues Vanden Bygaart et
al., (2003) observe that non-inversion tillage
physically protects part of the organic matter
in the top layer from mineralization by inclusion within macro-aggregates With conventional inversion tillage on the other hand, aggregates will be more thoroughly disrupted, assisting loss of organic matter
Mangalassery et al., (2014) revealed that zero
tilled soils contained significantly more soil organic matter (SOM) than tilled soils Soil from the 0–10 cm layer contained more SOM than soils from the 10–20 cm layers in both zero tilled (7.8 and 7.4% at 0–10 cm and 10–
20 cm respectively) and tilled soils (6.6% at 0–10 cm and 6.2% at 10–20 cm)
Temporal scales of soil C dynamics
Wang et al., (2016) also found that higher
amounts of C input can lead to higher soil C sink capacities On a global average, the total amounts of C input to soils are 1.7, 2.7 and3.7 MgC ha−1 under the crop residue retention rates of 30, 60 and 90 %, respectively Lal, (2004) reported that the rates of SOC sequestration in croplands range from 0.02 to 0.76 MgC ha−1 yr−1 when improved systems
of crop management are adopted However, it should be noted that the increased SOC sequestration rate that is contributed to by the increased C input can be limited at longer periods, as the SOC would eventually reach a
relatively stable threshold (Stewart et al.,
2007) On a global scale, the estimated efficiency of the conversion of C input to
Trang 8SOC is 14 %, which falls within the 10–18 %
range estimated by Campbell et al., (2000) It
should be noted that the conversion efficiency
varies across space and is highly dependent
on the local climatic and edaphic conditions
(Yu et al., 2012) Mangalassery et al., (2014)
observed that zero tilled soils contained
significantly more microbial biomass carbon
than tilled soils The mean microbial biomass
carbon under zero tilled soil was 517.0 mg kg
-1
soil compared with 418.7 mg kg-1 soil in
tilled soils Microbial biomass carbon was
significantly higher in the 0–10 cm layer (517
mg kg-1 soil) than the 10–20 cm layer (419
mg kg-1 soil) under zero tillage and
conventional tillage Moreover, tillage and
soil depth significantly influenced soil
microbial biomass nitrogen Zero tilled soils
contained higher microbial biomass nitrogen
(91.1 mg kg-1 soil) than tilled soil (70.0 mg
kg-1 soil) Surface layers (0–10 cm)
maintained more microbial biomass nitrogen
than sub surface layers (10–20 cm) under both
zero tilled soils and tilled soils
Fortuna et al., (2003a) found that addition of
organic nutrient sources like compost to the
soil for more than 6 years has the potential to
increase the pools of slow (10% increase) and
resistant (30% increase) C and the potential
pool of potentially mineralizable N West and
Post (2002) calculated that converting from
mouldboard plough to no-till sequestered an
additional 0.57±0.14 Mg Cha-1yr-1 of C and
complex crop rotations had the potential to
sequester an additional 20±12 gCm-2yr-1 of C
Seventeen ±15% of C applied in animal
amendments such as poultry manure becomes
part of soil organic matter (SOM) (Johnson et
al., 2009) Key management practices that
retain or return residues to the soil have been
shown to insulate and elevate soil
temperatures reducing the extremity and
frequency of freeze-thaw cycles leading to a
reduction in N2O emissions Soil C and N
dynamics are influenced to a greater degree
by quantity rather than quality of plant
residues Gentile et al., (2011) reported that
the quality of crop residues effects short term nutrient dynamics and has a less of an impact
on C sequestration Jha et al., (2012)
suggested that the addition of FYM to soil increased the active C pool to a greater extent
as compared to the slow and resistant C pools
Powlson et al., (2012) also found the effect of
reduced tillage and addition of different organic materials on soil C stocks and N2O emissions They found that reduced tillage practices increased the annual C stocks compared to conventional tillage However, this was compensated for increased N2O emissions under reduced tillage management
Dendooven et al., (2012) revealed that no till
with crop residue removal and conventional tillage with residue retention or removal were net sources of CO2, with a positive net GWP ranging from 1.288 to 1.885 Mg CO2
ha−1yr −1 Hence, no till when practiced with residue retention had higher N2O emissions but also increased the C storage to an extent that the systems had net negative GWP
Gattinger et al., (2012) concluded that the
SOC stocks and C sequestration rates were significantly higher in the zero net input organic farming systems as compared to non-organic cropping systems by 1.98 ±1.50 MgCha-1 and 0.07±0.08 MgCha-1yr-1(mean ± 85% confidence interval) respectively Palm
et al., (2014) reported that the combined
effect of types of crops, intensity of cropping, duration of the cropping systems, the amount
of inputs added to the systems in the form of residues and the tillage intensity along with soil properties like soil texture, temperature and moisture determines the overall soil C
and N turnover and storage Thomazini et al.,
(2015) reported that organic no till with leguminous intercropping and pre-plant compost application had the potential to immobilize C in microorganisms thereby promoting a positive C balance in the soil leading to a C sink and improved soil health
Trang 9Zhao et al., (2016) indicated that returning
corn straw to the soil along with mixing it
reduced the CO2 emissions and increased the
soil organic carbon content thereby improving
the composition of micro-aggregate better
than straw mulching Zhang et al., (2016)
indicated that the application of chemical
fertilizers plus manure could be a suitable
management for ensuring crop yield and
sustaining soil fertility but the ratio of
chemical fertilizers to manure should be
optimized to reduce C and N losses to the
environment
Tillage system influence on soil organic
carbon storage
Wang et al., (2018) reported that tillage
system change influenced SOC content, NT,
ST, and BT showed higher values of SOC
content and increased 8.34, 7.83, and
1.64 Mg·C·ha−1, respectively, compared with
CT Among the 3 changed tillage systems, NT
and ST showed a 12.5% and 11.6% increase
in SOC content then BT, respectively Tillage
system change influenced SOC stratification
ratio values, with higher value observed in BT
and NT compared CT but ST Therefore, in
loess soil, changing tillage system can
significantly improve SOC storage and
change profile distribution Naresh et al.,
(2018) reported that conservation tillage
practices significantly influenced the total soil
carbon (TC), Total inorganic carbon (TIC),
total soil organic carbon (SOC) and
oxidizable organic carbon (OC) content of the
surface (0–15 cm) soil Wide raised beds
transplanted rice and zero till wheat with
100% (T9) or with 50% residue management
(T8) showed significantly higher TC, SOC
content of 11.93 and 10.73 g kg-1,respectively
in T9 and 10.98 and 9.38 g kg-1, respectively
in T8 as compared to the other treatments
Irrespective of residue incorporation/
retention, wide raised beds with zero till
wheat enhanced 53.6%, 33.3%, 38.7% and
41.9% of TC, TIC, SOC and OC, respectively, in surface soil as compared to conventional tillage with transplanted rice cultivation Simultaneously, residue retention caused an increment of 6.4%, 7.4%, 8.7% and 10.6% in TC, TIC, SOC and OC, respectively over the treatments without residue management
Concerning the organic carbon storage, SOCs varied between 31.9 Mg·ha−1 and 25.8 Mg·ha−1 under NT, while, in tilled treatments, SOCs ranged between 28.8 Mg·ha−1 and 24.8 Mg·ha−1 These values were lower than those observed by
Fernández-Ugalde et al., (2009) who found,
in silty clay soil, a SOCs at 0–30 cm of 50.9 Mg·ha−1 after 7 years of no tillage, which was significantly higher than the 44.1 Mg·ha−1 under CT under wheat-barley
cropping system in semiarid area Hernanz et
al., (2009) also found, after 11 years under
NT, a SOCs of 37 Mg·ha−1 which was higher than 33.5 Mg·ha−1 under CT, using a wheat-
vetch (Vectoria sativa L.) rotation in silty soil
The lower SOCs values we observed can be explained by the fact that more time is needed before achieving the peak sequestration rate
under NT Xu et al., (2013) observed that the
SOC stocks in the 0–80 cm layer under NT was as high as 129.32 Mg C ha−1,significantly higher than those under PT and RT The order
of SOC stocks in the 0–80 cm soil layer was
NT > PT > RT, and the same order was observed for SCB; however, in the 0–20 cm soil layer, the RT treatment had a higher SOC stock than the PT treatment. Alemayehu et
al., (2016) also found that the carbon storage per hectare for the four soil textures at 0 to 15
cm depth were 68.4, 63.7, 38.1 and 31.3 tha-1for sandy loam, silt loam, loam and clay loam; respectively Sand and silt loams had nearly twice the organic carbon content than loam and clay loam soil The soil organic carbon content for tillage type at 0 to 15 cm was 8.6, 10.6, 11.8 and 19.8 g kg-1 for deep
Trang 10tillage, minimum tillage, shallow tillage, and
zero tillage; respectively Among tillage types
soil organic carbon storage could be increased
by using the minimum and shallow tillage
SOC storage decreased with soil depth, with a
significant accumulation at 0-20cm depth
Zheng et al., (2018) reported that across
treatments, aggregate-associated C at a depth
of 0–10cm was higher in the NT and ST
treatments than in the MP and CT treatments
The advantage of the NT treatment weakened
with soil depth, while the amount of
aggregate-associated C remained higher for
the ST treatment There were more
macro-aggregates in the ST and NT treatments than
in the MP and CT treatments, while the MP
and CT treatments had more
micro-aggregates The sum of macro-aggregate
contributing rates for soil organic C (SOC)
was significantly superior to that of the
micro-aggregates Mahajan et al., (2019) reported
that the increased SOC stock in the surface 50
kg m-2 under ZT and PRB was compensated
by greater SOC stocks in the 50-200 and
200-400 kg m-2 interval under residue retained, but
SOC stocks under CT were consistently lower
in the surface 400 kg m-2.Soil organic carbon
fractions (SOC), microbial biomasses and
enzyme activities in the macro-aggregates are
more sensitive to conservation tillage (CT)
than in the micro-aggregates Responses of
macro-aggregates to straw return showed
positively linear with increasing SOC
concentration Straw-C input rate and clay
content significantly affected the response of
SOC
Soil organic carbon and sequestration
SOM is a complex mixture which contributes
positively to soil fertility, soil tilth, crop
production, and overall soil sustainability It
minimizes negative environmental impacts,
and thus improves soil quality (Farquharson
et al., 2003) (Fig 4a) Loveland and Webb
(2003) suggested that a major threshold is 2%
SOC (ca 3.4% SOM) in temperate regions, below which potentially serious decline in soil quality will occur Storage of SOC is a balance between C additions from non-harvested portions of crops and organic amendments, and C losses, primarily through organic matter decomposition and release of respired CO2 to the atmosphere Organic matter returned to the soil, directly from crop residues or indirectly as manure, consists of many different organic compounds Some of these are digested quickly by soil microorganisms The result of this is a rapid formation of microbial compounds and body structures, important in holding particles together to provide soil structure and to limit soil erosion, and the release of carbon dioxide back to the atmosphere through microbial
respiration (Kladivko 2001) Paustian et al.,
(1998) compared tillage systems, ranging in duration from 5 to 20 years, and estimated that NT resulted in an average soil C increase
of 285 g/m2, compared to conventional tillage
(CT) Liu et al., (2003) showed a significant
decline of total SOC that occurred in the first
5 years of cultivation where the average SOC loss per year was about 2300 kg/ha for the 0–
17 cm horizon The average annual SOC loss between 5- and 14-year cultivation was 950 kg/ha and between 14- and 50-year cultivation it was 290 kg/ha These data clearly showed a rapid reduction of SOC for the initial soil disturbance by cultivation and a relatively gradual loss later Compared with
organic matter in the uncultivated soil, Liu et
al., (2003) also indicated that the total SOC
loss was 17%, 28%, and 55% in the 5-, 14- and 50-year cultivation periods, respectively The latter would correspond to the release of approximately 380 ton CO2/ha to the atmosphere
Within the surface 7.5 cm, the no-till system possessed significantly more SOC (by 7.28 Mg/ha), particulate organic matter C (by4.98 Mg/ha), potentially mineralizable N (by 32.4